It started with a seemingly innocent question, posted in an online forum on the Web site Fairfax Underground, in a new discussion thread titled “West Springfield High arrest.”

“3 students at this school where just arrested. Any reason why they couldn’t call them in do the principal office and arrested them after school ended?” asked the anonymous, grammatically challenged “Wshs student.”

As usual on Fairfax Underground, the post elicited profane insults, irrelevant tangents and not much new information. At first. But others joined the discussion, throwing out the rumors they’d heard at school and the names of students allegedly arrested for making videos of themselves having drunken sex with several girls. And then a television news reporter found the thread and went to the Fairfax County police, which confirmed that three sophomore boys had been charged with possession and distribution of child pornography.

Suddenly, the West Springfield High School’s sex tape scandal was all over TV, the radio talk shows, Twitter and Facebook, and it became the topic of discussion between countless appalled parents and their cellphone-wielding teens, all courtesy of Fairfax Underground.

While online forums are ubiquitous on the Web, they are usually topic based — places where people discuss bowling or beauty products or bondage. What makes Fairfax Underground unusual, experts say, is its geographical focus. It covers any topic, from the best place for laser surgery to Annandale back in the day to “outlandish” public school salaries to texting while driving on Interstate 66, as long as it is about Fairfax County.

In December, someone obtained and then posted on Fairfax Underground a 2,100-page document with the final class grades for thousands of Fairfax High School students. Fairfax County Public Schools quickly obtained a federal injunction ordering the document taken down.

The publishing of juveniles’ names troubles parents and those in the legal system who are accustomed to giving some protection to teenagers. And it troubles Cary Wiedemann, the 28-year-old founder of Fairfax Underground, who closely monitors and sometimes edits the postings on the site but does his best to keep what he happily describes as a “cesspool” as wild and free as possible.

In the West Springfield case, he said, the arrests were “a public event, in view of everybody, and everybody has the right to discuss it.”

“If anything’s being discussed anywhere on the streets, it’s fair game for Fairfax Underground.”

To be clear, there’s no legal question here. It is illegal for Virginia authorities to disclose the names of juveniles in court or school cases, but it is not illegal for a news outlet, blog or online forum to publish them. Most mainstream media have policies of not naming juveniles, although they occasionally suspend them, as was done with 17-year-old Lee Boyd Malvo after his arrest in the D.C. sniper shootings.

And Congress was quite explicit, as far back as the Communications Decency Act of 1996, that online hosts are not responsible for the content of posts from outside parties and may moderate or delete content without taking on legal liability.

But should Fairfax Underground, which Wiedemann says gets 1 million unique viewers per month and a thousand posts a day, have allowed the names of the kids to stay posted?

“I’m a big advocate of free speech,” said Mark J. Petrovich, a lawyer who represents one of the West Springfield students who was arrested and also represented Malvo. “But you have anonymous people posting things that aren’t true.”

In some posts, students who were not involved were accused. And there were allegations — which one school official told The Washington Post were false — that the girls were drugged and had not consented to the sex. None of the three suspects were charged with forcible sex crimes.

“There’s no accountability for that,” Petrovich said, “and when you start throwing kids under the bus, I don’t think anybody would want their kids subject to that.

Wiedemann said that he has monitored the West Springfield discussion thread and that when he identified one Internet provider address repeatedly posting false material under different user names, he appended a note to all of them: “Malicious user spreading misinformation. His 30 posts in this thread will be marked with this message.”

Petrovich scoffed. “Everyone goes right to those posts,” the lawyer said. “That exacerbates the situation.”

But to Wiedemann, a thoughtful, animated computer-systems manager, it’s all about transparency and freedom of speech. He removes posts only if they violate his basic ground rules: No personal attacks, no complete garbage, no impersonation. He will try to eliminate racist or extremely vile content if it appears to originate from outside Fairfax, and he has blocked all posters from Europe and Asia. But if you’re local and you want to say something, you can pretty much say it on Fairfax Underground.

Wiedemann first had the idea for a local site that would attract users and chatter by collecting Fairfax arrest data and making it searchable. The site went live in 2005 with the goal of being “completely honest, open and accessible to everybody.” No registration. No moving images. No up-or-down voting on posts. Just raw peer-to-peer chat, not sponsored by any corporation and free of advertising. Wiedemann makes no money and maintains the server himself.

“Fairfax Underground is a cesspool primarily because anonymous, unregistered users are allowed to post,” Wiedemann said. “But it’s a cesspool that accurately reflects the inner thoughts and motives of the community at large. Previously private prejudices can be exposed, and challenged, with impunity. The Internet is about peer-to-peer communication, without an editor’s lens or filters. My role is strictly to keep order and to dispel misinformation.”

In the case of the Fairfax school grades, there was no personal information such as addresses or Social Security numbers, so the data were merely embarrassing, not dangerous, Wiedemann argued. In the West Springfield episode, Fairfax police had not reported anything, so people came to Fairfax Underground for answers, he said.

Officer Eddy Azcarate said Fairfax police’s public information office “didn’t find out about the arrests until two weeks after they happened. We made the decision, because it’s an ongoing investigation and it’s juveniles, not to do a [press] release. With juveniles, there’s very little we can say anyway. We did respond to all inquiries as they came in.”

Various police officials monitor Fairfax Underground, if only to take the temperature of the community, but sometimes officers post requests for help or tips on an investigation. They recognize the power and pitfalls of the site. And so does its creator.

Over the years, Wiedemann has been a target for Fairfax Underground posters, whether for the unfettered nature of the site or his nearly 2,000 “edit by Cary” modifications or deletions of various postings. Some postings point out his own arrest record for traffic and marijuana-related ­offenses (one possession plea at age 19, one distribution charge dropped in 2010) ; he does not touch those.

“I have to have a thick skin, and I do,” said the Northern Virginia native and former Chantilly High student. “I don’t want people to think I treat myself any differently. But ultimate transparency is the key to everything, for our society to learn.

“I’m not trying to be a troublemaker. I’m legitimately trying to inform the community of what’s going on.”

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